When it comes to eye health and maintaining good vision over the span of your lifetime, there are three providers who you’re likely to interact with: ophthalmologists, optometrists and opticians. Known as the three Os, these professionals can be found all across the country peering into patients’ eyes to look for and correct vision and other health problems.

The human eye is such a complicated and delicate organ that it takes the efforts of all three to care for some patients. Ophthalmologists, optometrists and opticians all have different levels of training and areas of specialty. “The ophthalmologist is the most well-trained of the three,” says Dr. Stephanie Marioneaux, an ophthalmologist in private practice in Chesapeake, Virginia, and clinical spokesperson for the American Academy of Ophthalmology. Ophthalmologists are physicians, so that means “we typically have four years of college,” followed by four years of medical school.

After completing medical school, a would-be ophthalmologist goes on to complete an internship, followed by three years of an ophthalmology residency program, which Marioneaux says is a very competitive position to attain. “Not only was it very competitive getting into medical school, it’s also very competitive getting into ophthalmology residency programs because there’s not very many spots available.” Following residency training, some ophthalmologists go on to complete a fellowship, which may take one or more years to finish. Lastly, ophthalmologists complete a series of written and oral exams to become board-certified.

By the time an ophthalmologist has completed training, Marioneaux says, “we have been tested, retested and we have board certification to practice ophthalmology, which encompasses routine eye exams, fitting glasses and fitting contact lenses, in addition to providing surgery for patients. We are effectively the one-stop shop. When patients come to see an ophthalmologist, we can do everything. If we find a problem, we can take the patient to the operating room. If we diagnose something we can treat it.”

In all, Marioneaux says ophthalmologists typically have between 12 and 14 years of training that encompasses not just the eye, but the entire body. This is important, she says, because the eyes aren’t just windows to the soul — they can also act as a window to the rest of the body. “I can look into someone’s eye during an examination and identify problems with the heart, like endocarditis,” which is an infection of the inner lining of the heart. Metastatic cancer and leukemia, a cancer of the blood, can also sometimes be detected via the eyes. “Back in the day when HIV was new, ophthalmologists were the first ones to diagnose CMV retinitis,” an inflammation of the retina that causes blindness and “is one of the terrible complications of HIV.” Diabetes, melanoma, brain tumors, blood vessel occlusions, migraines and even sleep apnea are all sometimes diagnosed during an eye exam if the practitioner knows what to look for.

Marioneaux encourages patients to see an ophthalmologist for all eye care needs, not just the most serious conditions. “I think there have been some misconceptions that ophthalmologists are only for surgery and all of the front-line problems are handled by other professionals,” Marioneaux says. “But that is completely incorrect.” She says it’s important to be seen regularly by a doctor who has the training and experience to spot potential problems. “The challenge is that the human eye is so incredible that you can have excellent vision and still have a very serious problem.”

Because many people seem reluctant to get regular check-ups with an ophthalmologist or seem confused about the role of the ophthalmologist vs. optometrist, the AAO issued a recommendation that adults visit an ophthalmologist for vision screening by the time they’re 40. “If you’ve never been evaluated by the ophthalmologist, then you must be evaluated starting at age 40,” Marioneaux says. With that baseline exam completed, the ophthalmologist can tell you how often you should return. Much like being screened regularly for breast cancer or prostate cancer, seeing an ophthalmologist on a regular interval is important, she says, because “many, many, many things can affect your eyes and your vision may be the last indicator that there’s a problem.”

Glaucoma is a good example of a condition that may creep in without many symptoms. ” Glaucoma is carried in the genes,” and while some family members might not mention that they have it, others may never have symptoms but could have passed the disease on to you. “Because of the way it’s inherited, it doesn’t show up in every generation,” Marioneaux says. “It skips around, and if you’re not paying attention to the family member who slips away and puts in an eye drop, you won’t know.”

While ophthalmologists are medical doctors or doctors of osteopathic medicine (and carry the initials M.D. or D.O. after their names to indicate which degree they have), optometrists have the initials O.D. after their name, signifying that they’ve completed optometry school. “Optometry school is in no way comparable to medical school because they don’t do hospital rotations, they don’t have to take the MCATs to be admitted and the training is completely different,” Marioneaux says. “Medical school is very rigorous and highly competitive and we learn about the entire body. We don’t just learn about one organ system.”

Nevertheless, most Americans who get eye exams receive them from an optometrist. Samuel D. Pierce, a doctor of optometry in private practice in Trussville, Alabama, and president of the American Optometric Association, says that “doctors of optometry throughout the United States perform 70 percent of eye exams. If someone goes in and gets an eye exam for the first time, there’s a 70 percent chance they’ll be seeing a doctor of optometry.” One of the reasons why is because “we’re available in over 10,000 communities and 97 percent of the population live within 5 miles of an optometrist’s office, so we are very accessible.”

Optometrists “examine the eye and visual system for any vision problems, eye-related problems or eye diseases as well as eye-related systemic diseases,” he says, noting that diabetes and hypertension are two common conditions an optometrist may be called on to help a patient manage. He says he has also helped patients get treatment for other conditions that affect health beyond the eyes. “For example, I once found signs of a brain tumor in a patient, and it turned out that’s exactly what they had. That’s not uncommon. It happens all across the country almost daily.”

Optometrists also work in collaboration with primary care physicians in some instances, particularly when it comes to caring for people who have diabetes. Pierce says he’ll correspond with primary care doctors frequently to develop a baseline report on the health of a diabetic’s eyes when they’re first diagnosed and then subsequently as their eyes change to help guide the physician’s management of the condition. “Doctors of optometry work within the health care system and they work closely with other health care professionals. We’re not isolated.”

Pierce likens the difference between optometrists and ophthalmologists to that between psychologists and psychiatrists, and says that “the education route is different for optometry. After college, you go directly into optometry school and spend four years studying all the basic sciences and the eye.” He says some optometrists then go on to do a one-year residency while others go directly into practice. “This is very similar to dentistry where, after four years of dental school, you can either do specialization training or go out into practice.”

The American Board of Optometry offers board-certification to optometrists, and while no state requires optometrists to be board-certified, some optometrists pursue certification as a mark of excellence. But, “in order to practice anywhere in the United States, you must be licensed by a state board,” Pierce says. The criteria for licensing varies by state, but “you typically have to demonstrate knowledge of what your scope of practice is and that you understand the limitations of your licensure,” Pierce says. Continuing education is required to maintain licensure.

Optometrists are sometimes called the primary care doctors of the eye, and Pierce says that while ophthalmologists can also provide that sort of care, “they’re more tertiary care. They are surgeons,” who offer procedures that optometrists don’t. “There are some surgical procedures doctors of optometry can perform, but they typically do not involve general anesthesia. For example, if you had a piece of metal embedded in your cornea, I can certainly remove that. In some states doctors of optometry can do biopsies on lesions to rule out skin cancers,” but for more complicated procedures, such as needing a cataract removed or a retina repaired, you’ll need to see an ophthalmologist.

Pierce says a good optometrist will refer patients who need that sort of additional care. “I think unless you need surgery, an optometrist is the best route for your comprehensive eye exam, being fitted for glasses and contact lenses and vision therapy. Allow your optometrist to refer you to an ophthalmologist when you need surgery, because that’s what they specialize in.”

Finally, both ophthalmologists and optometrists often work closely with opticians. Bob Reynolds, president of the Opticians Association of America and a licensed dispensing optician in Atlanta, says “opticians are the face of eyewear.” Opticians make glasses and sometimes fit contact lenses. “We take a prescription from an M.D. or an optometrist and interpret and fill it,” and there’s more to making glasses than meets the eye. “The interpretation is a big part of it,” he says. “It’s not just plugging in numbers, it’s coming up with a design and producing a functioning, controlled medical device.” Opticians do not fill prescriptions for medications related to eye therapy, such as the drops used to treat glaucoma; filling those prescriptions would require the services of a pharmacist.

While many people may be more interested in the fashion side of choosing the right glasses, the mechanics of how the lenses help them see is the key part of helping people see better. An optician works with patients to make sure the frames and lenses work together to meet the needs of the prescription and that they fit properly.

Generally speaking, there are two paths to becoming an optician, Reynolds says — through schooling or through an apprenticeship. “I’m an educated optician,” meaning “I went to school and got a degree in ophthalmic dispensing.” These programs tend to take one to two years to complete, depending on the state and the student’s previous level of educational attainment. However, “not every state has a school, so there are apprentice programs in some states. I live in Georgia, so in addition to three opticianry schools, we also have an apprentice program that allows you to have a structured training period that is legally laid out.” This program requires apprentices to register with the secretary of state’s office and to be “sponsored by a licensed professional — either an ophthalmologist, an optometrist or an optician.” The training takes two years and results in licensure.

Again, training and licensure regulations vary from state to state, and Reynolds says that while Georgia has more stringent requirements for someone to practice as an optician, “our next-door neighbor, Alabama, has no standard or requirement for opticianry. Anyone can be plugged in and basically fill an eyeglasses prescription.” He says this is “a weakness in the system,” that the OAA is working to address by advocating for the institution of nationwide certification standards for opticians.

Reynolds says that opticians are often found in an ophthalmologist or optometrist’s office, but that they may also have their own stand-alone businesses. “It’s a team, and the team can be set up in any number of ways.” For example, Reynolds works “at an optician-owned practice, and we employ an optometrist. People usually think of it being the other way around where opticians work for optometrists, and that’s probably more common. Some opticians work for ophthalmologists and run their dispensaries,” and both optometrists and ophthalmologists need the support of an optician, Reynolds says, because they “aren’t really trained to do the dispensing side of it.”

When it comes time to get glasses, Reynolds recommends making sure that the optician you’re working with has the right training and experience to look after this important aspect of eye health. “We just want the public to understand that you don’t want someone who was selling shoes yesterday fitting you in a controlled medical device. There’s a lot more that goes into it — training and understanding what those numbers mean.”

In all cases, it’s important to keep an eye on the health of your eyes, because it can have implications for overall health. The three Os can make sure that you get the care you need. “The best scenario is when all three of us work together,” Marioneaux says.